Abstract: The communications between terminals are encrypted, and even a gateway device is permitted to analyze the encrypted communications, thereby to incarnate censorship for the prevention of information leakage. A gateway device 3 prepares a public key and a secret key in a pair on the basis of a public key encryption system, and distributes the public key to terminals 2a-2c which are managed by the gateway device 3. The terminals 2a-2c subject a communication packet to a prior-art common key encryption, and they thereafter encrypt a common key with the public key and bestow the encrypted common key on the packet. The gateway device 3 decrypts the common key by using the secret key, censors the packet and returns the packet into a prior-art encrypted packet format, and it thereafter transfers the packet to a network 1c where opposite terminals 2d-2f exist.

Abstract: With a system having no paging function, dead peer detection control and cutoff of a session are implemented as is the case with a system having a paging function. There is provided a method for dead peer detection of a mobile terminal, to be executed in a mobile communications system including a mobile terminal connected to plural wireless systems, a first connection device terminating a first wireless system with access points managing a connection status between the mobile terminal and a wireless link, and a second connection device terminating a second wireless system with access points not managing a connection status between the mobile terminal and a wireless link, said method comprising the steps of the second connection device acquiring the connection status of the mobile terminal in the first wireless system from the first connection device, and the second connection device changing a dead peer detection control process on the basis of the connection status of the mobile terminal, as acquired.

Abstract: With a system having no paging function, dead peer detection control and cutoff of a session are implemented as is the case with a system having a paging function. There is provided a method for dead peer detection of a mobile terminal, to be executed in a mobile communications system including a mobile terminal connected to plural wireless systems, a first connection device terminating a first wireless system with access points managing a connection status between the mobile terminal and a wireless link, and a second connection device terminating a second wireless system with access points not managing a connection status between the mobile terminal and a wireless link, said method comprising the steps of the second connection device acquiring the connection status of the mobile terminal in the first wireless system from the first connection device, and the second connection device changing a dead peer detection control process on the basis of the connection status of the mobile terminal, as acquired.

Abstract: The communications between terminals are encrypted, and even a gateway device is permitted to analyze the encrypted communications, thereby to incarnate censorship for the prevention of information leakage. A gateway device 3 prepares a public key and a secret key in a pair on the basis of a public key encryption system, and distributes the public key to terminals 2a-2c which are managed by the gateway device 3. The terminals 2a-2c subject a communication packet to a prior-art common key encryption, and they thereafter encrypt a common key with the public key and bestow the encrypted common key on the packet. The gateway device 3 decrypts the common key by using the secret key, censors the packet and returns the packet into a prior-art encrypted packet format, and it thereafter transfers the packet to a network 1c where opposite terminals 2d-2f exist.